Methods of preparing cemented metal carbide substrates for deposition of adherent diamond coatings and products made therefrom

ABSTRACT

Methods for producing an adherent diamond film on a cemented metal carbide substrate are disclosed. Particularly, the present invention discloses methods of preparing the surface of a cemented metal carbide surface such that an adherent polycrystalline diamond coating may be deposited thereon using CVD techniques. Cutting tool inserts produced from such adherent diamond film coated cemented metal carbide articles are also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to hard coatings for metal carbidesubstrates. More particularly, the present invention relates to a methodof producing an adherent diamond coating on cemented metal carbidearticles and the articles so coated.

2. Description of the Related Art

Polycrystalline diamond (PCD) cutting tools, comprising a piece ofpolycrystalline diamond fastened to the tip of a tool insert are old andwell-known in the art. These tools are expensive to manufacture and donot readily lend themselves to indexing for increased tool life. Inaddition, PCD tooling having complex shapes, i.e., taps, drill bits,end-mills, etc., cannot be easily formed using any known techniques. PCDtools are typically run at cutting speeds of around 2,500 SFM whencutting materials such as A-390 aluminum.

Numerous attempts have been made to provide diamond coated tools whichhave performance approaching that of PCD tools because they would beless costly to manufacture and use, and because diamond coated toolshaving more complex shapes than are possible with PCD tools aretheoretically manufacturable employing substrates such as cementedtungsten carbide.

A significant challenge to the developers of diamond-coated tooling isto optimize adhesion between the diamond film and the substrate to whichit is applied, while retaining sufficient surface toughness in thefinished product. Substrates like Si₃ N₄ and SiAlON can only be formedinto a few geometries, limiting their commercial potential. Sinteredtungsten carbide (WC) substrates without cobalt or other binders havebeen studied but can be too brittle to perform satisfactorily as toolingin machining applications.

Cemented tungsten carbide substrates incorporating a cobalt binder inconcentrations between about 2% and 20% weight % Co, and cubic carbidessuch as TiC, TaC, NbC, and VC, and combinations thereof inconcentrations up to about 30% by weight of Co, have the requisitetoughness and thus show the greatest long-term commercial promise fortooling applications. A cemented tungsten carbide substrate with up to20% cobalt, for example, would provide adequate surface toughness formost machining tasks. Cemented tungsten carbide can be formed into avariety of geometries, making it a potential material for drillingoperations, die manufacturing, and other applications of value to theautomobile and other industries. It is therefore desirable to provide away to coat cemented tungsten carbide substrates with a layer of diamondfilm having adequate adhesion to the substrate for use as a machinetool.

It has been reported in the literature that the use of a cobalt binderin cemented carbides inhibits adhesion of the diamond film to thesubstrate. (R. Haubner and B. Lux, Influence of the Cobalt Content inHot-Pressed Cemented Carbides on the Deposition of Low-Pressure DiamondLayers, Journal de Physique, Colloque C5, supplement au no. 5, pp.C5-156-169, Toma 50, (May 1989)). Indeed, conventional wisdom indicatesthat successful use of cemented tungsten carbide substrates may only beachieved by utilizing substrates containing no cobalt, as taught in U.S.Pat. No. 4,990,403; no more than 4% Co binder, as taught in U.S. Pat.No. 4,731,296, or by deliberately depleting the cobalt concentration atthe surface of the substrate. It is known to deplete the cobaltconcentration at the surface of the substrate by selective etching orother methods, (M. Yagi, Cutting Performance of Diamond Deposited Toolfor Al 18 mass % Si Alloy, Abst. of 1st Int. Conf. on the New DiamondSci. & Technol., pp. 158-159, Japan New Diamond Forum, (1988)), but thisdecreases the surface toughness of the substrate and can cause chippingof the substrate and applied diamond film. Increased adhesion of diamondto the substrate may be achieved by decarburizing the substrate prior todeposition, as taught in European Patent Application Publication No. 0384 011, but use of this procedure does not optimize substrate toughnessand does not lend itself well to manufacturing environments whererepeatability and consistency are important issues. The prior artteaches polishing or scratching the surface of a cemented tungstencarbide substrate prior to attempting diamond deposition due to theenhancement of the nucleation process caused by polishing andscratching. (Haubner and Lux (supra), Yagi (supra), M. Murakawa et al.,Chemical Vapor Deposition of a Diamond Coating Onto a Tungsten CarbideTool Using Ethanol, Surface and Coatings Technology, Vol. 36, pp.303-310, 1988; Kuo, et al., Adhesion and Tribological Properties ofDiamond Films on Various Substrates, J. Mat. Res., Vol. 5, No. 11,November 1990, pp. 2515-2523.) These articles either teach the use ofpolished substrates or indicate poor results obtained by utilizingsubstrates whose surfaces have not been prepared by polishing orscratching. A promising solution to the adhesion problem has been toemploy an interlayer between the diamond coating and the WC/Cosubstrate. This encapsulates the Co, optimizing adhesion while allowingthe substrate to retain its toughness. It may also be possible to choosean effective interlayer material that bonds strongly to diamond coating,further increasing adhesion. U.S. Pat. No. 4,707,384 discloses the useof a titanium carbide interlayer. U.S. Pat. Nos. 4,998,421 and 4,992,082disclose the utilization of a plurality of layers of separated diamondor diamond like particles interposed with layers of a planarized bondingmaterial.

Another solution to the adhesion problem is disclosed in U.S. Pat. No.5,236,740 issued Aug. 17, 1993 to Peters et al., wherein some of thetungsten carbide at the surface of a cemented tungsten carbide articleis etched away without removing any cobalt binder, and then in a secondetching step the residue from the first etching step is removed afterwhich a diamond coating is applied. The first etching step requires theuse of a strong base combined with a cyanide compound, and the secondetching step requires the use of a strong acid combined with a strongoxidizing compound.

It is also generally known in the cemented carbide industry that ferricchloride (FeCl₃) solutions will dissolve cobalt via theoxidation-reduction reaction Co+2Fe⁺³ →Co⁺² +2Fe⁺². However, the rate ofreaction, and most importantly, the uniformity of the depth of reactionaround an insert were not known.

General references regarding the chemical etchants for tungsten carbideand tungsten alloys include Annual Book of ASTM Standards, Part II,Metallography; Non-destructive Testing, American Society for Testing andMaterials, page 60 (etching reagent consisting of a mixture of 10 wt. %NaOH and 30 wt. % H₂ O₂ in a 2:1 ratio) & page 439 (various combinationsof acids for use as etchants--HF/HNO₃ /H₂ O, HF/HNO₃ /HCl and HF/HNO₃/lactic acid), (1979), and Metals Handbook, Vol. 8, American Society forMetals, 8th edition, page 109 (1973).

It would, however, be advantageous to develop methods to provide for theoptimum direct diamond coating of a cemented tungsten carbide articlehaving superior adhesion for machining purposes without the need toutilize cyanide components in the process. Tools of such diamond coatedcemented tungsten carbide articles would also be desirable.

OBJECTS AND SUMMARY OF THE INVENTION

One object of the present invention is to provide a process of producingan adherent diamond film on a cemented metal carbide substrate.

Another object of the present invention is to provide an adherentdiamond film on a cemented metal carbide substrate without the need touse cyanide compounds and strong acids.

Yet another object of the present invention is to produce improvedadherent diamond film coated cemented metal carbide substrates which maybe utilized as metal cutting tool inserts.

Still yet another object of the present invention is to produce improvedadherent diamond film coated cemented metal carbide substrates which maybe utilized as metal cutting tool inserts comprising preformed chipcontrol geometries.

Accordingly, one form of the present invention relates to a process forcoating cemented metal carbide substrates with a diamond film,comprising the steps of: performing a first etching step comprisingetching a cemented metal carbide substrate in a first chemical systemwhich selectively removes a portion of the cobalt binder; cleaning theetched surface of the cemented metal carbide substrate of said firstetching step; performing a second etching step comprising etching thecemented metal carbide substrate of the first cleaning step in a secondchemical system which selectively removes any surface metal carbidegrains, while providing substantially no etching of the cobalt binder,further characterized in that said second chemical system consists of anoxygen-containing anion; cleaning the etched surface of the cementedmetal carbide substrate of said second etching step; depositing asubstantially continuous diamond film on a desired portion of saidsurface of said cemented metal carbide substrate of the second cleaningstep.

Another form of the invention relates to a process for coating groundcemented metal carbide substrates with a diamond film, comprising thesteps of: performing a first etching step comprising etching a cementedmetal carbide substrate in a first chemical system which selectivelyremoves a portion of the cobalt binder; cleaning the etched surface ofthe cemented metal carbide substrate of said first etching step;performing a second etching step comprising etching the cemented metalcarbide substrate of the first cleaning step in a second chemical systemwhich selectively removes any surface metal carbide grains, whileproviding substantially no etching of the cobalt binder, furthercharacterized in that said second chemical system consists of anoxygen-containing anion; cleaning the etched surface of the cementedmetal carbide substrate of the second cleaning step; depositing asubstantially continuous diamond film on a desired portion of saidsurface of said cemented metal carbide substrate of the second cleaningstep.

Yet another form of the present invention relates to a process forcoating ground cemented tungsten carbide substrates with a diamond film,comprising the steps of: performing a first etching step comprisingetching a cemented tungsten carbide substrate in a first chemical systemwhich selectively removes a portion of the cobalt binder; cleaning theetched surface of the cemented tungsten carbide substrate of said firstetching step; performing a second etching step comprising etching thecemented tungsten carbide substrate of the first cleaning step in asecond chemical system which selectively removes any surface tungstencarbide grains, while providing substantially no etching of the cobaltbinder, further characterized in that said second chemical systemconsists of an oxygen-containing anion; cleaning the etched surface ofthe cemented tungsten carbide substrate of said second etching step;depositing a substantially continuous diamond film on a desired portionof said surface of said cemented tungsten carbide substrate of thesecond cleaning step.

Still another form of the present invention relates to the productproduced according to the process of the present invention.

Yet still another form of the present invention relates to a metalcutting insert produced according to the process of the presentinvention.

Preferred forms of the invention, as well as other embodiments, objects,features and advantages of this invention, will be apparent from thefollowing detailed description which is to be read in connection withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an SEM photomicrograph of a ground WC-6 wt % Co insert(5000X).

FIG. 2 is an SEM photomicrograph of a ground WC-6 wt % Co insert treatedin 0.05M FeCl₃ for 1.5 minutes, followed by ultrasonic cleaning (5000X).

FIG. 3 is an SEM photomicrograph of a ground WC-6 wt % Co insert, aftertreatment in a 0.05M FeCl₃ solution for 1.5 minutes, followed bytreatment in a 10 wt. % NaOH (75 ml)/30 wt. % H₂ O₂ (37.5 ml), initiallyat 50° C., for 3 minutes (5000X).

FIG. 4 is an optical photomicrograph of a cross-sectioned ground WC-6 wt% Co insert treated in 0.05M FeCl₃ for 71/2 minutes (1000X).

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be better understood from the specificationtaken in conjunction with the accompanying examples.

In the process of grinding cemented carbide inserts a great deal ofdamage to the surfaces is produced. FIG. 1 is a typical ground surfacewhen viewed perpendicular to the surface at approximately 5000Xmagnification with a scanning electron microscope. One can see grindmarks, some rather featureless areas consisting of truncated orfragmented WC grains, and some areas where "pull-out" of the grains hasoccurred. It is only in the latter areas that the deposited diamond filmcan adhere to the carbide substrate. While not wishing to be limited toany one theory, it is believed that the damaged metal carbide grains inthe top several microns of the ground insert surface need to be removedto expose well defined metal carbide grains which will allow one toachieve mechanically anchored, and hence adherent, diamond films.

It has now been surprisingly found that the desired removal of surfacegrains of tungsten carbide and the subsequent deposition of an adherentdiamond film can be achieved through a multi-step process. Generally,first the surface onto which the deposition of an adherent diamond filmis desired is treated with a first chemical system which selectivelyremoves the cobalt binder to a desired depth. It has been surprisinglyfound that treatments with ferric chloride, using the principle ofoxidation-reduction give consistent and uniform cobalt removal to thedesired depth. FIG. 2 is an SEM photomicrograph at a magnification of5000X of a ground cemented tungsten carbide insert having 6 wt. % cobaltafter treatment with a first chemical system comprising an aqueoussolution of 0.05M FeCl₃ for 1.5 minutes, followed by ultrasoniccleaning. Even though the cobalt binder has been etched to a depth ofapproximately 3 microns, there is very little change to the surface. TheWC grain have not been noticeably loosened, due presumably to theintimate interlocking of the grains. The etching of the cobalt binder toa specific depth prevents the graphitization of the deposited diamondfilm. The etching of the cobalt binder in the first step providesanother benefit in that the tungsten carbide grains are exposed to thesecond chemical system, and allows that reaction to proceed morerapidly.

Next, surface grains of tungsten carbide are selectively removed to adesired depth by utilizing a second chemical system which is furthercharacterized as consisting of an oxygen-containing anion. FIG. 3 is anSEM photomicrograph at a magnification of 5000X of a ground tungstencarbide insert having 6 wt. % cobalt after treatment in an aqueoussolution of 0.05M FeCl₃ for 1.5 minutes, followed by treatment in a 10wt. % NaOH (75 ml)/30 wt. % H₂ O₂ (37.5 ml) solution, initially at 50°C., for 3 minutes. As a result of such treatment, well-defined tungstencarbide grains, as seen in FIG. 3, were exposed. This morphologyresulted in improved mechanical anchoring, and hence improved adhesion,of the deposited diamond film.

Finally, the desired film is deposited upon the hereinabove preparedsurface using known diamond deposition procedures, especially CVDdeposition procedures.

According to one preferred aspect of the present invention, a method isdescribed for preparing a cemented tungsten carbide substrate forcoating with a layer of diamond film. In practice a cemented tungstencarbide substrate is etched in a first chemical system comprising asolution of FeCl₃ (ferric chloride) at room temperature. The exposedtungsten carbide grains, which are now free of cobalt binder, are thenetched using a second chemical system, characterized as consisting of anoxygen-containing anion, to remove these tungsten carbide grains andexpose as many tungsten carbide surfaces suitable for diamond filmnucleation sites as possible. Finally, the diamond film is depositedonto the prepared surface of the tungsten carbide substrate.

In one preferred embodiment of the present invention, the cementedtungsten carbide substrates are rinsed in de-ionized water,ultrasonically cleaned in deionized water, ultrasonically cleaned inethyl alcohol and then air dried after each etching step.

Cemented tungsten carbide substrates which are suitable for use in thepresent invention are those containing up to 30% by weight of cobalt,preferably, those containing from about 1% to about 16%, and mostpreferably those containing from about 3% to about 6% by weight ofcobalt. These types of cemented tungsten carbide substrates aregenerally associated with cutting tools but may be used for any suitablepurpose.

It has been surprisingly found that a first etching step comprisingetching in a first chemical system comprising a solution of a FeCl₃ atroom temperature does not substantially attack the metal carbide grainsbut does provide for the selective removal of the cobalt. Those skilledin the art will recognize that the depth of etching of the cobalt willdepend upon the molarity of the FeCl₃ solution, the temperature, thereaction time and the substrate composition (i.e., cobalt content,binder chemistry and carbide grain size), so that some reactionexperimentation is expected prior to industrial applications to defineoptimum parameters. The strength of the cutting edge is reduced due toetching of cobalt and therefore control of depth of etch is important.Certain machining operations such as milling which involve impact willbenefit from a shallower depth of etch as compared to less severeoperations such as straight turning which may be able to tolerate adeeper etch. The presently preferred solutions are about 0.05M and about0.10M FeCl₃ aqueous solution, but other concentrations known in the artmay also be used. The criterion is to reach a desired depth of cobaltremoval in an acceptable time period and in a reproducible manner, suchcriteria being well known in the art. The depth of cobalt removal is upto from about 2 microns to about 12 microns, and preferably from about 3to about 10 microns. An approximately 3 micron depth of cobalt removalmay be realized by immersing the selected cemented tungsten carbidesubstrate in a 0.05M FeCl₃ aqueous solution for 1.5 minutes at roomtemperature in the case of a grade C2 carbide, for example. Thoseskilled in the art will recognize that the preferred depth of cobaltremoval is dependent upon the end use to which the cemented substratewill be put, and the ranges given herein are not to be construed aslimiting, but rather are merely illustrative of use as a cutting tool.The concentration of FeCl₃ is in the range of from about 0.01M to about1M, depending upon preferred reaction times, temperatures and amount ofcobalt to be removed from the substrate. Those skilled in the art willrecognize that the chosen molarity of the FeCl₃ solution will depend onthe temperature, reaction time, and substrate composition (i.e., cobaltcontent, binder chemistry and carbide grain size), so that some reactionexperimentation is expected prior to industrial applications to defineoptimum parameters. The presently preferred solutions are about 0.05Mand about 0.10M FeCl₃ aqueous solution, but other concentrations knownin the art may also be used.

Other chemical systems which have been found suitable for use in thefirst etching step include sodium persulfate (Na₂ S₂ O₈), sodiumtetrafluoroborate (NaBF₄), sodium citrate (Na₃ C₆ H₅ O₇.2H₂ O), sodiumpyrophosphate (Na₄ P₂ O₇.10H₂ O), boric acid (H₃ BO₃), potassium sodiumtartrate ((KOOC)(CHOH)₂ (COONa).4H₂ O), ammonium hydroxide (NH₄ OH),acetic acid (HC₂ H₃ O₂), ammonium fluoride (NH₄ F), sodium dithionite(Na₂ S₂ O₄), sodium tri-phosphate (Na₅ P₃ O₁₀) and combinations thereof.These chemical systems all etch the cobalt binder substantially withoutattacking the metal carbide grains.

The criterion is to reach a desired depth of cobalt removal in anacceptable time period and in a reproducible manner, such criteria beingwell known in the art. Those skilled in the art will recognize that thepreferred depth of cobalt removal is dependent upon the end use to whichthe cemented substrate will be put, and the ranges given herein are notto be construed as limiting, but rather are merely illustrative of useas a cutting tool insert.

Concentrations of the chemical systems and the times and temperatures ofthe reactions may be easily determined by those skilled in the artwithout undue experimentation to meet desired operating parameters.

The discovery of suitable chemical compounds for use as the secondchemical system to selectively etch metal carbide grains began with theknown compounds for the etching of tungsten carbide and tungsten alloysin the hereinabove described references [Annual Book of ASTM Standards,Part II, Metallography; Non-destructive Testing, American Society forTesting and Materials, at page 60 and at page 439, and Metals Handbook,Vol. 8, American Society for Metals, 8th edition, at page 109]. However,it was quickly ascertained that strong acids (HCl, HNO₃, and HF, andcombinations thereof, for example) while indeed dissolving tungstencarbide, also dissolved the cobalt binder, and at a much more rapidrate. For example, complete removal of damaged tungsten carbide grainsfrom the surface of a ground WC-6 wt % Co (C2 carbide) insert using asolution of 1 part HF/5 parts HNO₃ /12 parts H₂ O at room temperaturetook only 11 minutes but etched the cobalt to a depth of 55 microns. Itwas also observed that the chemical attack on the cobalt binder wasquite non-uniform. The use of NaOH/H₂ O₂ solutions, however, proved toselectively attack tungsten carbide, but this reference did not teachhow to utilize this to provide a metal carbide substrate capable ofhaving an adherent diamond film deposited thereupon.

The presently preferred second etching step comprising etching in asecond chemical system comprising a 2:1 ratio of 10 wt. % NaOH and 30wt. % H₂ O₂ solution used at room temperature of about 20° C. forgreater than about 5 minutes, and preferably 15 to 60 minutes. Longeretching times are possible, but are limited by the reactivity of themixture. Other chemical systems which have been found suitable for usein the second etching step include aqueous solutions of hydrogenperoxide (H₂ O₂), sodium perborate (NaBO₃.4H₂ O), sodium chlorite(NaClO₂), tri-sodium phosphate (Na₃ PO₄.12H₂ O), sodium hydroxide(NaOH), sodium bicarbonate (NaHCO₃), sodium carbonate (Na₂ CO₃), sodiummetaborate (Na₂ B₂ O₄.8H₂ O), sodium borate (Na₂ B₄ O₇.10H₂ O), sodiumnitrite (NaNO₂), sodium phosphate dibasic (Na₂ HPO₄.7H₂ O), sodiumacetate (NaC₂ H₃ O₂.3H₂ O) and combinations thereof. This second etchingstep removes damaged metal carbide grains with substantially no attackof the cobalt binder. Concentrations of the chemical systems and thetimes and temperatures of the reactions may be easily determined bythose skilled in the art without undue experimentation to meet desiredoperating parameters.

The time of this etching step is dependent on the type of cementedtungsten carbide substrate, the solution type and the concentrationused. These parameters are well understood in the art and may beascertained by one skilled in the art without undue experimentation. Inorder for these chemical systems to etch the metal carbide grainsefficiently, it is preferred that the cobalt be etched with the firstchemical system, thus exposing the tungsten carbide grains to the secondchemical system.

The use of strong acids to perform the second etching step is to beavoided because strong acids tend to remove the cobalt binder to a depththat is greater than desired to produce a strong substrate for thediamond film deposition and for use as a cutting tool insert.

These surface preparation techniques are not limited to ground cementedcarbide products. It is expected that they will be suitable techniquesfor as-sintered cemented carbide products as well. In both situations,tungsten carbide (and solid solution carbide) grains are being removedfrom the surfaces; in the one case the grains are damaged, in the otherthey are not. Also, the substrate is not limited to tungsten carbide,but may also comprise titanium carbide, tantalum carbide, niobiumcarbide, vanadium carbide, and combinations thereof.

The adherent diamond film may be applied in any suitable known method.Suitable methods of applying an adherent diamond film include, but arenot limited to, for example, reactive vapor deposition,thermally-assisted (hot-filament) CVD, plasma-enhanced CVD, plasmaarc-jet CVD, as well as other known methods. The presently preferredmethod is the low-pressure plasma-enhanced CVD. The most commonly usedand widely studied method is the microwave plasma-assisted CVD. Theoperating conditions for this method are well-known in the art. Forexample, the following operating conditions are successfully applied:Microwave power=300 W to 75 KW, Substrate temperature (for cementedcarbide tools)=800° C. to 1200° C., Total Pressure=10⁻² torr to 10⁺²torr, CH₄ /H₂ ratio=0.1-10.0%. Total gas flow rate will depend upon thesize of the deposition chamber, use of other, non-reactive gases such asargon, and the nature and growth rate of deposited film desired. Methodsdescribed in the art fall generally within these parameters and areapplicable for depositing a diamond film.

Diamond films can be deposited from a variety of known carbon sources,such as aliphatic hydrocarbons and their variants which contain variousamounts of other species such as oxygen, nitrogen, halogens etc.Bachmann, et al (Diamond and Related Materials, Vol. 1, 1992, p. 1)teach that while it is eminently possible to deposit a good qualitydiamond film from a mixture of hydrogen and methane, the operatingdomain of useful deposition can be enlarged by the addition of smallamounts of oxygen to the gas. Indeed, practitioners of the art have usedadditions of gases such as pure O₂, CO, CO₂, as well as compounds suchas alcohols, ketones and the like. U.S. Pat. No. 4,816,286 lists a widerange of organic compounds containing carbon and hydrogen, withoptionally other elements such as oxygen, nitrogen and the like, invarious states of chemical bonding. Regrettably, however, it does notconclusively demonstrate that every one of the listed compounds actuallydeposits diamond using any of the listed methods of deposition in theirteaching. It is, therefore, left to the speculation of a practitioner todecide which of these compounds, which theoretically can producediamond, actually do so.

It has been amply demonstrated in the art, through thermodynamicmodeling methods and deposition trials, that the key ingredient in thesuccessful deposition of diamond from the vapor-phase mixture of ahydrocarbon and hydrogen is the methyl radical, CH₃. Methane provides asingle methyl radical during decomposition in the presence of atomichydrogen plasma generated by the action of the microwave energy. We havesurprisingly discovered that dimethyl ether, CH₃ OCH₃, is an efficientand energetic source of two active methyl radicals, as well as providingan oxygen atom which beneficially broadens the operating range of theprocess. While this discovery was surprising, it was by no meansunexpected, since it has been previously shown in the deposition ofW_(x) C compounds by CVD that dimethylether is indeed a better precursorthan alcohols and other hydrocarbons, as taught in Bhat and Holzl, ThinSolid Films, vol. 95, 1982, p. 105, and in U.S. Pat. No. 4,162,345, andU.S. Pat. Nos. 4,855,188; 4,874,642; 4,910,091 and 5,024,901.

While not subscribing to any one theory, it is believed that thechemical nature of the bonds which incorporate oxygen in the alcohols,i.e., bonding on one side with carbon and on the other with hydrogen inthe form of the OH radical, makes it more difficult to realize the fullreactivity and energy of the broken bonds during the synthesis process.On the other hand, the oxygen in dimethylether is symmetrically bondedon both sides to carbon atoms. Thus, when the carbon-to-oxygen bonds arebroken, one obtains a free oxygen ion and two methyl radicals. Possiblemechanisms of decomposition of methyl alcohol, ethyl alcohol anddimethylether are schematically shown below.

Decomposition of methyl alcohol (CH₃ OH): CH₃ OH→CH₃ +OH

Decomposition of ethyl alcohol (CH₃ CH₂ OH): CH₃ CH₂ OH→CH₃ +CH₂ +OH

Decomposition of dimethylether (CH₃ OCH₃):CH₃ OCH₃ →2CH₃ +O

It can be seen that the decomposition of alcohols can lead to therelease of the OH radical, which can combine during diamond depositionwith atomic hydrogen which is present in the reactor. This can lead tothe formation of water vapor. Condensation of water vapor in the colderregions of the reactor system can lead to operational problems. However,the use of dimethylether is advantageous in this regard. It is alsoadvantageous over using CO, CO₂, or even pure oxygen because of the easeof decomposition of dimethylether. In some vacuum systems, use of oxygencan cause serious degradation of vacuum pump oil unless expensive oilsare used instead of the conventional pump oil. Thus, it is found thatdimethylether is an excellent source of carbon and oxygen, and allows afiner control of gas-phase chemistry and quality of diamond film. Thepresently preferred method is to utilize a partial pressure ofdimethylether of from about 1% to about 5% in a mixture of dimethyletherand hydrogen at an operating pressure of from about 10 torr to about 50torr, and most preferably a partial pressure of from about 1.5% to about3.0% of dimethylether at about 25 torr total pressure. Depending on thesize of the deposition reactor and other operating parameters of thedeposition system, other ranges of concentrations and pressures as wellas other conditions will become apparent to those skilled in the arthaving the benefit and knowledge of conditions given heretofore.Therefore, the presently preferred conditions are not intended to belimiting the scope of this invention and other, obvious and deducedvariations are intended to fall within the scope of this invention.

The following examples are intended to be illustrative of variousaspects of the invention, and are not to be construed as limiting in anyway the scope and spirit of the invention.

EXAMPLES Example 1

Two C2 grade (WC-6 wt % Co) cemented tungsten carbide cutting toolinserts were used in the as-sintered condition. Two different strengthFeCl₃ etching solutions were prepared. One solution comprised 4.05 gramsof anhydrous FeCl₃ dissolved in 250 ml of deionized water to provide a0.10M solution. The second solution comprised 20.2 grams of anhydrousFeCl₃ was dissolved in 250 cc of deionized water to provide a 0.50Msolution. One insert was treated in each FeCl₃ solution at roomtemperature for 1 minute with gentle agitation of the solution. Eachinsert was then rinsed in deionized water and then placed in anultrasonic cleaning system for 10-15 seconds in a beaker containingdeionized water. Finally, they were rinsed in ethyl alcohol and allowedto air dry. Each insert was then cross-sectioned and polished andexamined by photomicrography. The examination of the cross-sectionedinsert exposed to the 0.10M FeCl₃ solution showed cobalt removal todepths of approximately 2 microns, and that the cross-sectioned insertexposed to the 0.50M FeCl₃ solution showed cobalt removal to depths ofapproximately 4 microns.

Example 2

Two cemented tungsten carbide cutting tool inserts having coarse-grainedtungsten carbide and 11 wt. % cobalt binder were used in the as-sinteredcondition. They were treated with the same FeCl₃ solutions and examinedas the samples in Example 1. The cross-sectioned insert exposed to the0.10M FeCl₃ solution showed cobalt etching to depths of approximately 3microns and the cross-sectioned insert exposed to the 0.50M FeCl₃solution showed cobalt etching to depths of approximately 10 microns.

Example 3

Ground C2 grade (WC-6 wt % Co) inserts, style SPG422, from a lot of 200inserts, were treated in a freshly prepared 0.05M FeCl₃ solution. Thesolution was prepared by adding 3.35 grams of FeCl₃.6H₂ O to 250 ml ofde-ionized water. The inserts were etched for times of 1, 2, 3, 4, 5,71/2 and 10 minutes with gentle agitation of the solution. Thesubsequent processing steps were as described in Example 1. The depthsof etch were found to be 2, 3-4, 5-6, 7-8, 9-10, 14-15 and 18-20microns, respectively. The depth of cobalt etch was shown to be linearwith time. Also, the depth of etch was remarkably uniform around theexposed surfaces of any given insert. A photomicrograph of thecross-sectioned insert treated for 71/2 minutes is shown in FIG. 4.

The following experiments illustrate additional chemical systems whichare suitable for selectively etching the cobalt binder of a cementedmetal carbide insert. All of the examples utilized cemented tungstencarbide inserts, style SPG 422, C2 grade, from a lot of 200 groundinserts all comprising tungsten carbide with 6 wt % Co binder.

Examples 4-14

Inserts from the batch of 200 were treated with various chemical systemsthat were found to be capable of selectively etching the cobalt binderwithout attacking the tungsten carbide grains. In each case the insertswere treated in an aqueous solution using deionized water and aftertreatment cross-sectioning was performed to allow optical microscopicexamination of the treated inserts. The specific chemical systems,experimental conditions, and the results of the chemical treatments aresummarized in Table 1 below.

                  TABLE 1                                                         ______________________________________                                        Summary of Cobalt Binder Etching Systems                                                           Depth of        Tempera-                                                      Cobalt   Time of                                                                              ture of                                  Chemical   Conc.     Etch     Reaction                                                                             Reaction                                 ______________________________________                                        Sodium persul-                                                                           10    wt. %   250    8 hours                                                                              75° C.                          fate Na.sub.2 S.sub.2 O.sub.8                                                                          microns                                              Sodium tetra-                                                                            3.3   wt. %   66     14 hours                                                                             75° C.                          fluoroborate             microns                                              NaBF.sub.4                                                                    Sodium citrate                                                                           10    wt. %   35     17 hours                                                                             75° C.                          Na.sub.3 C.sub.6 H.sub.5 O.sub.7.2H.sub.2 O                                                            microns                                              Sodium     6.7   wt. %   19     15 hours                                                                             75° C.                          pyrophosphate            microns                                              Na.sub.4 P.sub.2 O.sub.7.10H.sub.2 O                                          Boric acid 5     wt. %   17     14 hours                                                                             75° C.                          H.sub.3 BO.sub.3         microns                                              Potassium Sodium                                                                         10    wt. %   6      15 hours                                                                             75°                             tartrate                 microns                                              (KOOC)                                                                        (CHOH).sub.2                                                                  (COONa).4H.sub.2 O                                                            Ammonium   10    vol. %  20     3 days Room                                   hydroxide                microns       Temp.                                  NH.sub.4 OH                                                                   Acetic acid                                                                              10    vol. %  30     51/2days                                                                             Room                                   HC.sub.2 H.sub.3 O.sub.2 microns       Temp.                                  Ammonium fluor-                                                                          10    wt. %   8      2 days Room                                   ide NH.sub.4 F           microns       Temp.                                  Sodium dithionite                                                                        5     wt. %   80     22 days                                                                              Room                                   Na.sub.2 S.sub.2 O.sub.4 microns       Temp.                                  Sodium tri-phos-                                                                         5     wt. %   70     20 days                                                                              Room                                   phate Na.sub.5 P.sub.3 O.sub.10                                                                        microns       Temp.                                  ______________________________________                                    

Examples 15-29

We searched for chemical systems that would remove the surface tungstencarbide grains from ground carbide substrates without substantiallyattacking the cobalt binder. Relatively inexpensive and safe chemicalsystems were pursued. Inserts from a batch of 200 ground, unhoned, WC-6wt % Co (C2) inserts were used in these exploratory studies.

In order to assess the many chemical systems that were attempted, andthen to rank the successful ones, we adopted a cobalt etching procedureconsisting of freshly prepared 0.05M FeCl₃ solutions for 1.5 minuteswhich gave a depth of etch of approximately 3 microns. After ultrasoniccleaning, rinsing and drying, the insert was weighed.

In each case the inserts were treated one at a time in an aqueoussolution using de-ionized water. The progress of the reaction wasmonitored at appropriate intervals by removing the insert from the testsolution and placing it in an ultrasonic cleaning system for 10-15seconds in a beaker containing de-ionized water. Debris was usually seencoming off the insert especially during the first time in the ultrasoniccleaning system. After rinsing and drying of the insert the weight losswas recorded. From optical examination of the top rake face atapproximately 100X, an estimate could be made of the amount of theoriginal surface that had been removed. Examination at approximately700X allowed the quality of the individual grains to be assessed.

The insert was returned to the test solution, and the process continueduntil the original surface had been removed. At this point, opticalexamination at approximately 700X revealed well-defined WC grains overthe entire surface. Examination at 5000X in a scanning electronmicroscope revealed surfaces that were essentially identical to thatshown in FIG. 4.

Cross-sectioning of the insert was then performed in order to determineif additional etching of the cobalt binder had occurred.

Insert weight losses were typically 4.0 mg for those situations wherecomplete removal of the surface had occurred. It was instructive toperform a simple calculation. A weight loss of 4.0 mg corresponded to avolume loss of 0.000256 cm³, using the density of WC equal to 15.6g/cm³. Since the exposed surface area of a SPG422 insert (top rake faceand the four flank faces) was 3.22 cm², the thickness of WC removed was0.000080 cm or 0.8 microns.

The successful chemical systems, experimental conditions, and theresults of the treatments are summarized in Table 2 below.

                  TABLE 2                                                         ______________________________________                                        Summary of Tungsten Carbide Etching Systems                                                     Time Required to Remove                                                       Damaged WC Grains                                                                   Room     50°                                   Chemical    Conc.       Temp.    C.   75° C.                           ______________________________________                                        Hydrogen    30/10   wt. %   111/2  3    --                                    peroxide/Sodium                                                                           1:2     ratio   minutes                                                                              min-                                       hydroxide   37.5    ml/75          utes                                       H.sub.2 O.sub.2 /NaOH                                                                             ml                                                        Hydrogen peroxide                                                                         50      wt. %   75     5    50                                    H.sub.2 O.sub.2             minutes                                                                              min- seconds                                                                  utes                                       Hydrogen peroxide                                                                         30      wt. %   115    8    72                                    H.sub.2 O.sub.2             minutes                                                                              min- seconds                                                                  utes                                       Hydrogen peroxide                                                                         3       wt. %   41/2   24   51/2                                  H.sub.2 O.sub.2             hours  min- minutes                                                                  utes                                       Sodium perborate                                                                          3.5     wt. %   95     50   10                                    NaBO.sub.3.4H.sub.2 O       minutes                                                                              min- minutes                                                                  utes                                       Sodium chlorite                                                                           5       wt. %   51/2   125  9                                     NaClO.sub.2                 hours  min- minutes                                                                  utes                                       Tri-sodium  10      wt. %   6 days --   6 hours                               phosphate                                                                     Na.sub.3 PO.sub.4.12H.sub.2 O                                                 Sodium hydroxide                                                                          10      wt. %   10 days                                                                              --   56 hours*                             NaOH                                                                          Sodium      8.6     wt. %   20 days**                                                                            --   10 hours                              bicarbonate                                                                   NaHCO.sub.3                                                                   Sodium carbonate                                                                          6.7     wt. %   21 days                                                                              --   13 hours                              Na.sub.2 CO.sub.3                                                             Sodium metaborate                                                                         10      wt. %   30 days                                                                              --   16 hours                              Na.sub.2 B.sub.2 O.sub.4.8H.sub.2 O                                           Sodium borate                                                                             6.7     wt.     (50%   --   16 hours                              Na.sub.2 B.sub.4 O.sub.7.10H.sub.2 O                                                                      complete                                                                      in 50                                                                         days)                                             Sodium nitrite                                                                            5       wt. %   (40%   --   16 hours                              NaNO.sub.2                  complete                                                                      in 50                                                                         days)                                             Sodium phosphate                                                                          5       wt.%    --     --   23 hours                              dibasic                                                                       Na.sub.2 HPO.sub.4.7H.sub.2 O                                                 Sodium acetate                                                                            25      wt. %   --     --   29 hours                              NaC.sub.2 H.sub.3 O.sub.2.3H.sub.2 O                                          ______________________________________                                         *Etching of the cobalt binder has also occurred; final depth 16 microns.      **Etching of the cobalt binder has also occurred; final depth 5 microns. 

Some comments about the H₂ O₂ /NaOH system are in order. After severalexperiments had been performed it became clear that the extent of thereaction of the surface tungsten carbide depended on the amount of H₂ O₂in the mixture, and that once the H₂ O₂ was consumed, there was nofurther reaction. Thus, for these exploratory experiments, we settled on75 ml of NaOH and 37.5 ml of H₂ O₂ as the components of the 2:1 10 wt %NaOH/30 wt % H₂ O₂ mixture.

Also, the reaction between this mixture and cemented carbides was foundto be quite exothermic. For example, with one SPG422 insert placed inthe above solution initially at room temperature, the temperature andthe bubbling activity at the insert surface increased over the next fewminutes. At the 3-minute mark the bubbling was so vigorous it could bestbe described as "frothing" which rose to a height of about one inch inthe 500 ml beaker. The temperature at this point was approximately 60°C. The temperature of the solution continued to rise to 68° C. at the41/2-minute mark while the "frothing" decreased. The bubbling at theinsert surfaces was still quite vigorous. The temperature slowly fell toapproximately 50° C. at the 15-minute mark, and bubbling was stilloccurring at the insert surfaces.

If larger quantities of inserts are to be treated by this procedure,then, clearly, the extent of removal of the surface WC grains willdepend upon the number of inserts, size of the inserts, volume andconcentration of H₂ O₂, volume and concentration of NaOH, initialtemperature, temperature excursions and time.

Solutions of sodium peroxide (Na₂ O₂) and water are expected to behavein a similar manner as mixtures of H₂ O₂ and NaOH, because sodiumperoxide reacts with water to produce H₂ O₂ and NaOH.

None of the other systems, including hydrogen peroxide solutions,exhibited any temperature increases during WC-surface removal.

All of the second chemical systems set forth herein gave rise to surfacemorphologies essentially identical to that shown in FIG. 3. It isreasonable to expect that all such treated substrates would, whensubjected to diamond deposition, give rise to adherent diamond films.

Example 30

A C2 insert from the 200-insert lot was treated in a freshly prepared0.05M FeCl₃ solution for 1.5 minutes. It was weighed and then subjectedto a 10 wt. % NaOH(75 ml)/30 wt. % H₂ O₂ (37.5 ml) solution. Thetemperature rise, the "frothing", and the temperature fall have beendescribed earlier. After 15 minutes, the insert was ultrasonicallycleaned, rinsed and dried. The weight loss was found to be 5.1 mg, whichwas more than the weight loss required to just remove the damagedsurface WC grains. Examination at 100X showed that all the grind markshad vanished, and at 750X, well-defined WC grains were visible.Cross-sectioning showed traces of the original depth of etch of thecobalt.

Another C2 insert from the same lot was treated exactly as describedabove, except that the insert was left in the solution for 3 hours,rather than 15 minutes. At the end of this time the weight loss wasfound to be 5.3 mg. There was complete removal of the original surfacewhen examined at 100X, and well-defined WC grains could be seen at 750X.Cross-sectioning again showed that traces of the original etch.

Thus, in the first case the reaction continued until essentially all ofthe H₂ O₂ had been exhausted from the solution. Leaving the insert inthe solution for several more hours did not cause additional attack ofthe tungsten carbide or of the cobalt.

Examples 31-34

These four examples demonstrate that the loss of weight of the cementedcarbide insert depends on the amount of H₂ O₂ in the NaOH/H₂ O₂ mixture.In all four experiments a 2:1 ratio of 10 wt. % NaOH and 30 wt. % H₂ O₂was used on samples as used in the previous examples and treated infreshly prepared 0.05M FeCl₃ solutions for 1.5 minutes. The timerequired for the bubbling to cease was determined, and the weight losseswere measured. The only difference in the four examples were the volumesof the components. Example 31 used 75 ml of NaOH and 37.5 ml of H₂ O₂,Example 32 used one quarter of these quantities, Example 33 used onehalf these quantities, and Example 34 used twice these quantities. Theresults are summarized below in Table 3.

                  TABLE 3                                                         ______________________________________                                                        Vol. of                                                                       Components   Time Required                                    Example                                                                              Mixture  (10% NaOH/30%                                                                              for Bubbling                                                                            Weight                                 No.    Ratio    H.sub.2 O.sub.2)                                                                           to Cease  Loss                                   ______________________________________                                        31     2:1        75 ml/37.5 ml                                                                            49 minutes                                                                              0.0065                                                                        grams                                  32     2:1      18.7 ml/9.3 ml                                                                             18 minutes                                                                              0.0024                                                                        grams                                  33     2:1      37.5 ml/18.7 ml                                                                            21 minutes                                                                              0.0047                                                                        grams                                  34     2:1      150 ml/75 ml 68 minutes                                                                              0.0073                                                                        grams                                  ______________________________________                                    

In the Example 32, only 50-60% of the original surface had been removed,and this was reflected in the weight loss. In the other threeexperiments there was sufficient H₂ O₂ in the solutions to more thancompletely remove the original damaged surfaces.

Examples 35-36

Studies were performed with mixtures other than the usual 2:1 ratio of10 wt % NaOH and 30 wt % H₂ O₂. We arbitrarily chose a 5:1 ratio using250 ml of NaOH and 50 ml of H₂ O₂. A ground WC-6 wt % Co insert from theusual source was treated in a freshly prepared 0.05M FeCl₃ solution for1.5 minutes and then weighed. The temperature of the solution (bothcomponents were at 21° C. initially) rose very rapidly to 32° C., andthere was vigorous bubbling at the insert surfaces. The temperature ofthe solution slowly rose to 38° C. and then slowly fell to 30° C. overthe duration of the experiment (70 minutes). Approximately every 10minutes the insert was transferred to a smaller beaker of de-ionizedwater and placed in the ultrasonic cleaner for 10-15 seconds.

At the 70-minute mark the weight loss was found to be 4.1 mg and therewas complete removal of the original ground surface. Cross-sectioningshowed traces of the original etch; i.e., no additional etching of thecobalt occurred.

We also arbitrarily chose a 2:30 ratio, using volumes of 7 ml of NaOHand 105 ml of H₂ O₂. A ground insert from the usual source was treatedin a freshly prepared 0.05M FeCl₃ solution for 1.5 minutes and thenweighed. The temperature of the solution slowly increased to 33° C., andthe bubbling activity also slowly increased until the experiment wasstopped at the 105-minute mark. The weight loss was 4.0 milligrams, andthere was essentially complete removal of the original ground surface.Cross-sectioning again showed traces of the original etch.

Clearly, the extent of removal of the surface WC grains depended uponthe number of inserts, size of inserts, volume and concentration of H₂O₂, volume and concentration of NaOH, temperature, temperatureexcursions and time.

Examples 37-38

Etching of the cobalt binder to a specific depth prevents thegraphitization of the subsequently deposited diamond film. Theseexamples show that etching of the cobalt binder in the first stepprovides another benefit in that the tungsten carbide grains are exposedto the etchant in the next step, and allows that reaction to proceedmore rapidly.

In one experiment a C2 insert from the same source as the previousexamples was treated in a freshly prepared 0.05M FeCl₃ solution for theusual 1.5 minutes. The insert was weighed after rinsing, ultrasoniccleaning and drying. It was then placed in a beaker containing 50 ml of30% H₂ O₂ at 21° C. The progress of the reaction was monitored after100, 110 and 115 minutes. Complete removal of the surface WC grains hadoccurred at that point as judged by optical examination of the insert.The weight loss was found to be 4.0 mg.

In another experiment, a C2 insert from the same source was weighedafter cleaning in ethyl alcohol. It was not treated in a ferric chloridesolution. It was placed in a beaker containing 50 ml of 30 wt % H₂ O₂ at21° C. The progress of the reaction was monitored after 120, 140, 160and 170 minutes. Complete removal of the WC grains occurred after 170minutes as judged by optical examination. The weight loss at this pointwas also found to be 4.0 mg.

Thus, etching first with ferric chloride solution substantially reducedthe time required to completely remove the original ground surface.

Examples 39-43

These examples show the applicability of the present invention for usewith cemented metal carbide substrates having a wide range of cobaltbinder content. The substrate samples had compositions of tungstencarbide-3 wt. % cobalt, fine grained tungsten carbide-6 wt. % cobalt,tungsten carbide-6 wt. % cobalt of the same grain size as the substratesdescribed in the hereinabove examples, tungsten carbide-10 wt. % cobalt,and tungsten carbide-16 wt. % cobalt, respectively. Each sample wascleaned and then etched in 0.05M FeCl₃ solutions to produce an etchingdepth of 3-4 microns in a similar manner to that described in the aboveexamples. The times necessary to produce these depths of etch were 1, 1,11/2, 2, and 4 minutes, respectively, for the five samples. The sampleswere cleaned, dried and reweighed. Next, each sample was treated in a6.7 wt. % sodium carbonate solution (20.1 grams of Na₂ CO₃ in 300 gramsof de-ionized water) at 75° C. Each sample was occasionally transferredto a beaker containing de-ionized water and placed in the ultrasoniccleaner. The process was continued until the original ground surfaceswere just removed. The times required to remove the damaged WC grainswere 35, 17, 131/2, 8, and 4 hours, respectively, for the five samples.The results are summarized in Table 4 below.

                                      TABLE 4                                     __________________________________________________________________________    Weights and Weight Losses of WC-Co Compositions After                         Treatments in FeCl.sub.3, and Hot Na.sub.2 CO.sub.3 Solutions                                Weight     Weight                                                             after      after                                                              FeCl.sub.3                                                                          Weight                                                                             Na.sub.2 CO.sub.3                                                                   Weight                                                 Weight                                                                              Treatment                                                                           Loss Treatment                                                                           Loss                                          Composition                                                                            (grams)                                                                             (grams)                                                                             (grams)                                                                            (grams)                                                                             (grams)                                       __________________________________________________________________________    WC-3 wt % CO                                                                           7.0540                                                                              7.0533                                                                              0.0007                                                                             7.0491                                                                              0.0042                                        WC-6 wt % CO                                                                           6.8648                                                                              6.8637                                                                              0.0011                                                                             6.8605                                                                              0.0032                                        (fine                                                                         grain)                                                                        WC-6 wt % Co                                                                           6.9268                                                                              6.9257                                                                              0.0011                                                                             6.9229                                                                              0.0028                                        WC-10 wt % Co                                                                          6.7304                                                                              6.7285                                                                              0.0019                                                                             6.7241                                                                              0.0044                                        WC-16 wt % Co                                                                          6.4682                                                                              6.4634                                                                              0.0048                                                                             6.4608                                                                              0.0026                                        __________________________________________________________________________

The cobalt losses which occurred after the FeCl₃ treatments areunderstandable. For approximately the same etching depth, one wouldexpect the weight loss for WC-3 wt. % Co to be the lowest and that forWC-16 wt. % Co to be the highest.

The weight losses associated with the dissolution of the surface WCgrains were found to be approximately the same. The average weight lossof 3.4mg corresponds to a volume loss of 0.00022cm³, using the densityof WC equal to 15.6 g/cm³. Since the exposed surface area of the samplesubstrates was 3.22 cm², the average thickness of WC removed during thehot sodium carbonate treatment was 0.000068 cm or approximately 0.7microns.

Examples 44-46

These examples show the applicability of the present invention for usewith cemented metal carbide containing solid solution carbides. Thesubstrate samples had compositions of 6.0 wt. % Co, 6.0 wt. % TaC,balance WC (style SPG 432); 6.0 wt. % Co, 15.0 wt. % TaC, 12.0 wt. %TiC, balance WC (dimensions 1/2×1/2×0,260 inches); and 9.8 wt. % Co,14.8 wt. % TaC, 6.5 wt. % TiC, balance WC (style SPG 422). Each samplewas cleaned and then etched in 0.05M FeCl₃ solutions and produced anetching depth of 3-4 microns in a similar manner to that described inthe above examples. The time necessary to produce this depth of etchingwas 11/2, 11/2 and 2 minutes, respectively, for the three samples TheNa₂ CO₃ in 300 grams of de-ionized water) at 75° C. Each sample wasoccasionally transferred to a beaker containing de-ionized water andplaced in the ultrasonic cleaner. The process was continued until theoriginal ground surfaces were just removed as evidenced by examinationat 750X using an optical microscope and at 10,000X using a scanningelectron microscope which showed well defined tungsten carbide and solidsolution carbide grains. The times required to remove the damaged WCgrains were 15, 13, and 5 hours, respectively, for the three samples.The results are summarized in Table 5 below.

                  TABLE 5                                                         ______________________________________                                        Weights and Weight Losses of WC-Solid Solution Carbide                        Compositions after Treatments in FeCl.sub.3 and Hot Na.sub.2 CO.sub.3         Solutions                                                                                      Weight Loss                                                                              Weight Loss after                                                  after FeCl.sub.3                                                                         Na.sub.2 CO.sub.3                                                  Treatment  Treatment                                         Composition      (milligrams)                                                                             (milligrams)                                      ______________________________________                                        WC-6 wt % Co-6 wt % TaC                                                                        1.8        2.9                                               WC-6 wt % Co-15 wt % TaC-                                                                      2.6        2.5                                               12 wt % TiC                                                                   WC-9.8 wt % Co-14.8 wt %                                                                       2.7        1.2                                               TaC-6.5 wt % TiC                                                              ______________________________________                                    

In summary, the two step etching method of the present invention removedthe surface and/or damaged carbide grains from the surfaces of a widerange of cemented carbide compositions. Further, the presence of solidsolution carbide grains appeared to have negligible influence on thetime required to accomplish this surface grain removal goal.

Example 47

Ten tool inserts of grade C2 (nominal composition 94 wt % WC-6 wt % Co),style SPG 422, were etched in a 1000 ml quantity of freshly preparedsolution of 0.1M FeCl₃ with constant stirring to give a depth of etch of4-5 microns. This was followed by rinsing twice in de-ionized water, andthen in ethyl alcohol. The second etching step was performed on five ofthe tools treated in the first step. The tools were placed in a 1000 mlbeaker containing 50 ml of 10 wt % NaOH solution, to which 25 ml of 30wt % H₂ O₂ were slowly added. The beaker was placed in a water bath tominimize the temperature increase and frothing. The temperature of thesolution rose to about 65° C. in three minutes, and then decreased toabout 40° C. after about 7 minutes. The inserts were removed from theetching solution after 15 minutes, ultrasonically cleaned, rinsed anddried. Examination of the top rake surfaces at high magnificationrevealed surfaces which were similar to that shown in FIG. 3.

One of the etched inserts was placed in an ASTeX HPMS 1.5 KW microwaveplasma CVD reactor operating at a frequency of 2.45 GHz. The chamber wasevacuated to a pressure of about 25 torr and a hydrogen plus 3% methaneplasma was initiated at a power of 1 KW. The reactant flow rate was 200sccm. The temperature of the tool was measured by a "Mirage" Infra-redpyrometer manufactured by IRCON, and was found to be approximately 900°C. throughout the deposition. The thickness of the diamond filmdeposited was approximately 10 μm, and the crystallographic orientationof the film was <100>.

The coated tool was subjected to machining tests. In the turning test,the parameters were: speed=2000 surface feet per minute (sfm),feed=0,010 inches per revolution (ipr), depth of cut (doc)=0.060 inches,work-piece material=aluminum-silicon alloy A-390. Flood coolant wasdirected at the tool/work-piece contact point during machining. Threecorners of the tool were tested under these conditions, and an averagetool life of about 1 minute was obtained. The cause of tool failure waswear-induced chipping. There was no delamination of the diamond coating.

In the milling test, the parameters were: speed=1645 sfm, feed=0.0105inches per tooth (ipt), doc=0,100 inch per pass. A 6" diameter,single-tooth cutter was used to test a single tool at a time in themilling of the A-390 alloy. No coolant was used in this test. The toolcompleted five passes without failure. The acceptance criterion in thistest was five passes without spalling of the coating or chipping of thecutting edge.

For comparison, a commercially available diamond-coated C-2 carbide toolhaving approximately 10 μm thick diamond coating with a <111> crystalorientation was tested in these tests. In turning, the tool lasted about1 minute and failed by spalling of the coating. In milling, the toolfailed after five passes due to spalling of the coating.

Example 48

Tools were etched as described in example 47, except that thetemperature of the second etching solution was maintained atapproximately 50° C., and the etching time was about 120 minutes. One ofthese tools was coated in the diamond deposition reactor as described inexample 47. For the first four hours of deposition, the concentration ofmethane in hydrogen was 1.5%. Under these conditions, the diamond filmwas deposited with a predominant <111> orientation. Following depositionat 1.5% methane concentration, the conditions were changed to 3% methaneconcentration for the last six hours. Under these conditions, thediamond film grew in the <100> orientation. After a total of ten hoursof deposition, the thickness of diamond film was approximately 20 μm.The temperature of deposition during the first four hours was about 920°C., and during the next six hours was about 915° C. The tool was testedin turning as described in example 47. A tool life of about 6 minuteswas obtained. The failure mode was wear. There was no spalling of thecoating.

Example 49

Tool inserts etched as described in example 48 were placed in thediamond deposition reactor, as described in example 47. A mixture ofhydrogen and dimethylether was used for diamond deposition. Theconcentration of dimethylether was 3% of total flow and the depositiontemperature was approximately 900° C. The thickness of diamond filmafter a deposition time of 7 hours was about 13 μm and the crystalorientation was <100>. Turning test as described in example 47 gave atool life of about 1 minute. Tool failure was due to wear-inducedchipping. There was no spalling of the diamond coating.

Example 50

Another tool insert was prepared as described in example 48 and coatedin the diamond deposition reactor using the following parameters:concentration of dimethylether=1.5%, substrate temperature=890° C.deposition time=7 hours The thickness of diamond coating was about 8 μm,and the orientation was <111>.

Example 51

Several tool inserts were prepared as described in example 48, and sentto an outside vendor for diamond deposition using the vendor's microwaveplasma CVD process. A thickness of approximately 25 μm was depositedwith a crystal orientation of predominantly <111>. A turning test asdescribed in example 47 was performed on one of the tools. The toollasted for about 7 minutes before failure due to slight chipping. Therewas no spalling of the diamond coating.

Example 52

Ten inserts of C2 grade, style SPG 422, were etched in a freshlyprepared solution of 0.05M FeCl₃ solution with constant stirring to givea depth of etch of approximately 4 microns. The tools were rinsed twicein de-ionized water, and in alcohol. Five of these tools were thenetched in a mixture of 50 ml of 10 wt % NaOH+25 ml of 30 wt % H₂ O₂ in a1000 ml beaker for about 180 minutes. The etching temperature was about50° C. The tools thus prepared were sent to an outside vendor fordiamond coating. This vendor used the hot-filament CVD method fordepositing diamond coatings, which were about 25 to 30 μm thick. One ofthese coated tools was tested in turning using the following parameters:speed=2000 sfm, feed=0.005 ipr, doc=0.020 inch, work-piecematerial=A-390 alloy. The tool lasted about 7.5 minutes before failuredue to wear. There was no spalling of the diamond coating.

Example 53

Thirty tool inserts of grade C2, style TPG 322, were etched in freshlyprepared 0.1M FeCl₃ solution for 5 minutes with constant stirring togive depths of etch of 8-9 microns. The inserts were then rinsed asdescribed in example 47. Eight of the tools from the first step wereplaced in a 1000 ml beaker containing 100 ml of freshly prepared 10 wt %NaOH solution at 50° C., to which 50 ml of 30 wt % H₂ O₂ were addedslowly. The temperature increased to about 80° C. in about 5 minutes.After ten minutes, the temperature dropped to about 65° C. The etchingprocess was carried out for a total of 60 minutes.

These tools were sent to an outside vendor for diamond deposition usingthe microwave plasma CVD method. The coating thickness was about 25 μm.One of the coated tools was tested in turning as described in Example47. The average tool life was about 17 minutes. The tool failed by wear.There was no spalling of the diamond coating.

What is claimed is:
 1. A process for coating cemented metal carbidesubstrates with a diamond film, comprising the steps of:a) performing afirst etching step comprising etching a cemented metal carbide substratein a first chemical system which selectively removes a portion of thecobalt binder; b) cleaning the etched surface of the cemented metalcarbide substrate of step a); c) performing a second etching stepcomprising etching the cemented metal carbide substrate of step b) in asecond chemical system which selectively removes any surface metalcarbide grains, while providing substantially no etching of the cobaltbinder, further characterized in that said second chemical systemincludes of an oxygen-containing anion; d) cleaning the etched surfaceof the cemented metal carbide substrate of step c); e) depositing asubstantially continuous diamond film on a desired portion of saidsurface of said cemented metal carbide substrate of step d).
 2. Aprocess for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 1 wherein, said cemented metal carbidesubstrate is unpolished.
 3. A process for coating a cemented metalcarbide substrate with a diamond film as claimed in claim 1 wherein,said cemented metal carbide substrate is polished.
 4. A process forcoating a cemented metal carbide substrate with a diamond film asclaimed in claim 1 wherein, said cemented metal carbide substratecontains up to about 30 wt. % cobalt binder.
 5. A process for coating acemented metal carbide substrate with a diamond film as claimed in claim1 wherein, said cemented metal carbide substrate contains from about 3wt. % to about 16 wt. % cobalt binder.
 6. A process for coating acemented metal carbide substrate with a diamond film as claimed in claim1 wherein said metal carbide substrates are selected from the groupconsisting of tungsten carbide, titanium carbide, tantalum carbide,niobium carbide, vanadium carbide, and combinations thereof.
 7. Aprocess for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 6 wherein said metal carbide is tungstencarbide.
 8. A process for coating a cemented metal carbide substratewith a diamond film as claimed in claim 1 wherein, said first chemicalsystem is an aqueous solution containing a chemical compound selectedfrom the group consisting of, ferric chloride, sodium persulfate, sodiumtetrafluoroborate, sodium citrate, sodium pyrophosphate, boric acid,potassium sodium tartrate, ammonium hydroxide, acetic acid, ammoniumfluoride, sodium dithionite, sodium tri-phosphate, and combinationsthereof.
 9. A process for coating a cemented metal carbide substratewith a diamond film as claimed in claim 1 wherein, said second chemicalsystem comprises at least one metal compound in solution selected fromthe group consisting of, hydroxides, peroxides, perborates, chlorites,carbonates, bicarbonates, metaborates, borates, acetates, phosphates,nitrites, and combinations thereof.
 10. A process for coating a cementedmetal carbide substrate with a diamond film as claimed in claim 1wherein, said second chemical system comprises at least one metalcompound in solution selected from the group consisting of, hydrogenperoxide, sodium peroxide, sodium perborate, sodium chlorite, tri-sodiumphosphate, sodium hydroxide, sodium bicarbonate, sodium carbonate,sodium metaborate, sodium borate, sodium nitrite, sodium phosphatedibasic, sodium acetate, and combinations thereof.
 11. A process forcoating a cemented metal carbide substrate with a diamond film asclaimed in claim 1 wherein, said second chemical system comprises anaqueous solution of two metal compounds.
 12. A process for coating acemented metal carbide substrate with a diamond film as claimed in claim10 wherein, said second chemical system comprises an aqueous solution ofa sodium hydroxide and hydrogen peroxide.
 13. A process for coating acemented metal carbide substrate with a diamond film as claimed in claim1 wherein, said etching step a) comprises etching with an aqueoussolution of ferric chloride.
 14. A process for coating a cemented metalcarbide substrate with a diamond film as claimed in claim 1 wherein,said first etching of step a) is carried out at a temperature of fromabout 20° C. to about 80° C.
 15. A process for coating a cemented metalcarbide substrate with a diamond film as claimed in claim 1 wherein,said second etching of step c) is carried out at a temperature of fromabout 20° C. to about 80° C.
 16. A process for coating a cemented metalcarbide substrate with a diamond film as claimed in claim 13 wherein,said first chemical system of step a) comprises an aqueous solution offrom about 0.01M to about 1M ferric chloride.
 17. A process for coatinga cemented metal carbide substrate with a diamond film as claimed inclaim 12 wherein, said second chemical system of step c) comprises anaqueous solution consisting of a 2:1 ratio of 10 wt. % NaOH and 30 wt.%. H₂ O₂.
 18. A process for coating a cemented metal carbide substratewith a diamond film as claimed in claim 1 wherein, said step a) iscarried out for a period sufficient to remove the desired amount ofcobalt binder which is dependent upon the concentration of the etchant,reaction temperature, cobalt content of the substrate, binder chemistry,and the carbide grain size.
 19. A process for coating a cemented metalcarbide substrate with a diamond film as claimed in claim 18 wherein,said step a) is carried out for a period of at least 11/2 minutes wherethe etchant comprises 0.05M FeCl₃ solution, at room temperature, andwherein the cemented metal carbide substrate is a grade C2 carbide. 20.A process for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 1 wherein, step b) and step d) comprise rinsingand ultrasonic cleaning of the substrate in de-ionized water, and finalrinsing in ethyl alcohol.
 21. A process for coating a cemented metalcarbide substrate with a diamond film as claimed in claim 20 wherein,said ultrasonic cleaning in step b) and step d) is carried out for aperiod of at least 10 seconds.
 22. A process for coating ground cementedmetal carbide substrates with a diamond film, comprising the steps of:a)performing a first etching step comprising etching a cemented metalcarbide substrate in a first chemical system which selectively removes aportion of the cobalt binder; b) cleaning the etched surface of thecemented metal carbide substrate of step a); c) performing a secondetching step comprising etching the cemented metal carbide substrate ofstep b) in a second chemical system which selectively removes damagedsurface metal carbide grains, while providing substantially no etchingof the cobalt binder, further characterized in that said second chemicalsystem includes an oxygen-containing anion; d) cleaning the etchedsurface of the cemented metal carbide substrate of step c); e)depositing a substantially continuous diamond film on a desired portionof said surface of said cemented metal carbide substrate of step d). 23.A process for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 22 wherein, said cemented metal carbidesubstrate is unpolished.
 24. A process for coating a cemented metalcarbide substrate with a diamond film as claimed in claim 22 wherein,said cemented metal carbide substrate is polished.
 25. A process forcoating a cemented metal carbide substrate with a diamond film asclaimed in claim 22 wherein, said cemented metal carbide substratecontains up to about 30 wt. % cobalt binder.
 26. A process for coating acemented metal carbide substrate with a diamond film as claimed in claim22 wherein, said cemented metal carbide substrate contains from about 3wt. % to about 16 wt. % cobalt binder.
 27. A process for coating acemented metal carbide substrate with a diamond film as claimed in claim22 wherein, the metal carbide substrates are selected from the groupconsisting of tungsten carbide, titanium carbide, tantalum carbide,niobium carbide, vanadium carbide, and combinations thereof.
 28. Aprocess for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 27 wherein the metal carbide consists oftungsten carbide.
 29. A process for coating a cemented metal carbidesubstrate with a diamond film as claimed in claim 22 wherein, said firstchemical system is an aqueous solution containing a chemical compoundselected from the group consisting of, ferric chloride, sodiumpersulfate, sodium tetrafluoroborate, sodium citrate, sodiumpyrophosphate, boric acid, potassium sodium tartrate, ammoniumhydroxide, acetic acid, ammonium fluoride, sodium dithionite, sodiumtri-phosphate, and combinations thereof.
 30. A process for coating acemented metal carbide substrate with a diamond film as claimed in claim22 wherein, said second chemical system comprises at least one metalcompound in solution selected from the group consisting of, hydroxides,peroxides, perborates, chlorites, carbonates, bicarbonates, metaborates,borates, acetates, phosphates, nitrites, and combinations thereof.
 31. Aprocess for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 22 wherein, said second chemical systemcomprises at least one metal compound in solution selected from thegroup consisting of, hydrogen peroxide, sodium peroxide, sodiumperborate, sodium chlorite, tri-sodium phosphate, sodium hydroxide,sodium bicarbonate, sodium carbonate, sodium metaborate, sodium borate,sodium nitrite, sodium phosphate dibasic, sodium acetate, andcombinations thereof.
 32. A process for coating a cemented metal carbidesubstrate with a diamond film as claimed in claim 22 wherein, saidsecond chemical system comprises an aqueous solution of two metalcompounds.
 33. A process for coating a cemented metal carbide substratewith a diamond film as claimed in claim 31 wherein, said second chemicalsystem comprises an aqueous solution of sodium hydroxide and hydrogenperoxide.
 34. A process for coating a cemented metal carbide substratewith a diamond film as claimed in claim 22 wherein, said etching step a)comprises etching with an aqueous solution of ferric chloride.
 35. Aprocess for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 22 wherein, said first etching of step a) iscarried out at a temperature of from about 20° C. to about 80° C.
 36. Aprocess for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 22 wherein, said second etching of step c) iscarried out at a temperature of from about 20° C. to about 80° C.
 37. Aprocess for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 34 wherein, said first chemical system of stepa) comprises an aqueous solution of from about 0.01M to about 1M ferricchloride.
 38. A process for coating a cemented metal carbide substratewith a diamond film as claimed in claim 33 wherein, said second chemicalsystem of step c) comprises an aqueous solution consisting of a 2:1ratio of 10 wt. % NaOH and 30 wt. % H₂ O₂.
 39. A process for coating acemented metal carbide substrate with a diamond film as claimed in claim22 wherein, said step a) is carried out for a period sufficient toremove the desired amount of cobalt binder which is dependent upon theconcentration of the etchant, reaction temperature, cobalt content ofthe substrate, binder chemistry, and the carbide grain size.
 40. Aprocess for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 39 wherein, said step a) is carried out for aperiod of at least 11/2 minutes where the etchant comprises 0.05M FeCl₃solution, at room temperature, and wherein the cemented metal carbidesubstrate is a grade C2 carbide.
 41. A process for coating a cementedmetal carbide substrate with a diamond film as claimed in claim 22wherein, step b) and step d) comprises rinsing and ultrasonic cleaningof the substrate in de-ionized water, and final rinsing in ethylalcohol.
 42. A process for coating a cemented metal carbide substratewith a diamond film as claimed in claim 41 wherein, said ultrasoniccleaning in step b) and step d) is carried out for a period of at least10 seconds.
 43. A process for coating a cemented metal carbide substratewith a diamond film as claimed in claim 1 wherein, the continuousdiamond film of said step e) is a substantially continuous CVDpolycrystalline diamond film characterized in that the carbon source forthe production of the diamond film is selected from the group comprisingaliphatic hydrocarbons, aliphatic hydrocarbons containing oxygen, andmixtures thereof with hydrogen.
 44. A process for coating a cementedmetal carbide substrate with a diamond film as claimed in claim 22wherein, the continuous diamond film of said step e) is a substantiallycontinuous CVD polycrystalline diamond film characterized in that thecarbon source for the production of the diamond film is selected fromthe group comprising aliphatic hydrocarbons, aliphatic hydrocarbonscontaining oxygen and mixtures thereof with hydrogen.
 45. A process forcoating a cemented metal carbide substrate with a diamond film asclaimed in claim 1 wherein, the continuous diamond film of said step e)is a substantially continuous CVD polycrystalline diamond filmcharacterized in that the carbon source for the production of thediamond film is dimethyl ether.
 46. A process for coating a cementedmetal carbide substrate with a diamond film as claimed in claim 22wherein, the continuous diamond film of said step e) is a substantiallycontinuous CVD polycrystalline diamond film characterized in that thecarbon source for the production of the diamond film is dimethyl ether.47. A process for coating ground cemented tungsten carbide substrateswith a diamond film, comprising the steps of:a) performing a firstetching step comprising etching a cemented tungsten carbide substrate ina first chemical system which selectively removes a portion of thecobalt binder; b) cleaning the etched surface of the cemented tungstencarbide substrate of step a); c) performing a second etching stepcomprising etching the cemented tungsten carbide substrate of step b) ina second chemical system which selectively removes damaged surfacetungsten carbide grains, while providing substantially no etching of thecobalt binder, further characterized in that said second chemical systemincludes an oxygen-containing anion; d) cleaning the etched surface ofthe cemented tungsten carbide substrate of step c); e) depositing asubstantially continuous diamond film on a desired portion of saidsurface of said cemented tungsten carbide substrate of step d).
 48. Aprocess for coating a cemented tungsten carbide substrate with a diamondfilm as claimed in claim 47 wherein, said cemented tungsten carbidesubstrate is unpolished.
 49. A process for coating a cemented tungstencarbide substrate with a diamond film as claimed in claim 47 wherein,said cemented tungsten carbide substrate is polished.
 50. A process forcoating a cemented tungsten carbide substrate with a diamond film asclaimed in claim 47 wherein, said cemented tungsten carbide substratecontains up to about 30 wt. % cobalt binder.
 51. A process for coating acemented tungsten carbide substrate with a diamond film as claimed inclaim 47 wherein, said cemented tungsten carbide substrate contains fromabout 3 wt. % to about 16 wt. % cobalt binder.
 52. A process for coatinga cemented tungsten carbide substrate with a diamond film as claimed inclaim 47 wherein, first chemical system is an aqueous solutioncontaining a chemical compound selected from the group consisting of,ferric chloride, sodium persulfate, sodium tetrafluoroborate, sodiumcitrate, sodium pyrophosphate, boric acid, potassium sodium tartrate,ammonium hydroxide, acetic acid, ammonium fluoride, sodium dithionite,sodium tri-phosphate, and combinations thereof.
 53. A process forcoating a cemented tungsten carbide substrate with a diamond film asclaimed in claim 47 wherein, said second chemical system comprises atleast one metal compound in solution selected from the group consistingof, hydroxides, peroxides, perborates, chlorites, carbonates,bicarbonates, metaborates, borates, acetates, phosphates, nitrites, andcombinations thereof.
 54. A process for coating a cemented tungstencarbide substrate with a diamond film as claimed in claim 53 wherein,said second chemical system comprises at least one metal compound insolution selected from the group consisting of, hydrogen peroxide,sodium peroxide, sodium perborate, sodium chlorite, tri-sodiumphosphate, sodium hydroxide, sodium bicarbonate, sodium carbonate,sodium metaborate, sodium borate, sodium nitrite, sodium phosphatedibasic, sodium acetate, and combinations thereof.
 55. A process forcoating a cemented tungsten carbide substrate with a diamond film asclaimed in claim 47 wherein, said second chemical system comprises anaqueous solution of two Group I alkali metal compounds.
 56. A processfor coating a cemented tungsten carbide substrate with a diamond film asclaimed in claim 53 wherein, said second chemical system comprises anaqueous solution of sodium hydroxide and hydrogen peroxide.
 57. Aprocess for coating a cemented tungsten carbide substrate with a diamondfilm as claimed in claim 47 wherein, said step d) comprises etching withan aqueous solution of ferric chloride.
 58. A process for coating acemented tungsten carbide substrate with a diamond film as claimed inclaim 47 wherein, said first etching of step a) is carried out at atemperature of from about 20° C. to about 80° C.
 59. A process forcoating a cemented tungsten carbide substrate with a diamond film asclaimed in claim 47 wherein, said second etching of step c) is carriedout at a temperature of from about 20° C. to about 80° C.
 60. A processfor coating a cemented tungsten carbide substrate with a diamond film asclaimed in claim 57 wherein, said first chemical step of step a)comprises an aqueous solution of from about 0.01M to about 1M ferricchloride.
 61. A process for coating a cemented tungsten carbidesubstrate with a diamond film as claimed in claim 56 wherein, saidsecond chemical system of step c) comprises an aqueous solutionconsisting of a 2:1 ratio of 10 wt. % NaOH and 30 wt. %.H₂ O₂.
 62. Aprocess for coating a cemented tungsten carbide substrate with a diamondfilm as claimed in claim 47 wherein, said step a) is carried out for aperiod sufficient to remove the desired amount of cobalt binder which isdependent upon the concentration of the etchant, reaction temperature,cobalt content of the substrate, binder chemistry and the tungstencarbide grain size.
 63. A process for coating a cemented tungstencarbide substrate with a diamond film as claimed in claim 57 wherein,said step a) is carried out for a period of at least 11/2 minutes wherethe etchant comprises 0.05M FeCl₃ solution, at room temperature, andwherein the cemented metal carbide substrate is a grade C2 carbide. 64.A process for coating a cemented metal carbide substrate with a diamondfilm as claimed in claim 47 wherein, step b) and step d) comprisesrinsing and ultrasonic cleaning of the substrate in de-ionized water,and final rinsing in ethyl alcohol.
 65. A process for coating a cementedmetal carbide substrate with a diamond film as claimed in claim 64wherein, said ultrasonic cleaning in step b) and step d) is carried outfor a period of at least 10 seconds.
 66. A process for coating acemented tungsten carbide substrate with a diamond film as claimed inclaim 47 wherein, the continuous diamond film of said step e) is asubstantially continuous CVD polycrystalline diamond film characterizedin that the carbon source for the production of the diamond film isselected from the group comprising aliphatic hydrocarbons, alipatichydrocarbons containing oxygen, and mixtures thereof with hydrogen. 67.A process for coating a cemented tungsten carbide substrate with adiamond film as claimed in claim 66 wherein, the continuous diamond filmof said step e) is a substantially continuous CVD polycrystallinediamond film characterized in that the carbon source for the productionof the diamond film is dimethyl ether.
 68. A process for coating acemented metal carbide substrate with a diamond film as claimed in claim1, wherein the depth of cobalt binder removal is from about 2 to about12 microns.
 69. A process for coating a cemented metal carbide substratewith a diamond film as claimed in claim 22 wherein the depth of cobaltbinder removal is from about 2 to about 12 microns.
 70. A process forcoating a cemented metal carbide substrate with a diamond film asclaimed in claim 47 wherein the depth of cobalt binder removal is fromabout 2 to about 12 microns.